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  1. Yue ZL, Feng YQ, Ng SW
    Acta Crystallogr C Struct Chem, 2015 Feb;71(Pt 2):100-2.
    PMID: 25652275 DOI: 10.1107/S2053229614028125
    In the linear coordination polymer catena-poly[[[aqua(1,10-phenanthroline-κ(2)N,N')copper(II)]-μ-pyridine-2,6-dicarboxylato-κ(4)O(2):O(2'),N,O(6)-[(nitrato-κ(2)O,O')bismuth(III)]-μ-pyridine-2,6-dicarboxylato-κ(4)O(2),N,O(6):O(6')] dihydrate], {[Bi(III)Cu(II)(C7H3NO4)2(NO3)(C12H8N2)(H2O)]·2H2O}n, the Bi(III) cation is O,N,O'-chelated by the two pyridine-2,6-dicarboxylate ligands and O,O'-chelated by the nitrate anion, the nine coordinating atoms conferring a tricapped trigonal prismatic environment on the metal centre. Each pyridine-2,6-dicarboxylate ligand uses one of its carboxylate O atoms to bind to an aqua(1,10-phenanthroline)copper(II) unit, the Cu-O dative bonds giving rise to the formation of a ribbon motif. The Cu(II) cation exhibits a square-pyramidal geometry. The ribbon motif propagates along the shortest axis of the triclinic unit cell and the solvent water molecules are hydrogen bonded to the same ribbon.
  2. Setifi Z, Lehchili F, Setifi F, Beghidja A, Ng SW, Glidewell C
    Acta Crystallogr C Struct Chem, 2014 Mar;70(Pt 3):338-41.
    PMID: 24594730 DOI: 10.1107/S2053229614004379
    In the title salt, C14H18N2(2+) · 2C9H5N4O(-), the 1,1'-diethyl-4,4'-bipyridine-1,1'-diium dication lies across a centre of inversion in the space group P21/c. In the 1,1,3,3-tetracyano-2-ethoxypropenide anion, the two independent -C(CN)2 units are rotated, in conrotatory fashion, out of the plane of the central propenide unit, making dihedral angles with the central unit of 16.0(2) and 23.0(2)°. The ionic components are linked by C-H...N hydrogen bonds to form a complex sheet structure, within which each cation acts as a sixfold donor of hydrogen bonds and each anion acts as a threefold acceptor of hydrogen bonds.
  3. Setifi F, Geiger DK, Abdul Razak I, Setifi Z
    Acta Crystallogr C Struct Chem, 2015 Aug;71(Pt 8):658-63.
    PMID: 26243410 DOI: 10.1107/S2053229615012437
    Polynitrile anions are important in both coordination chemistry and molecular materials chemistry, and are interesting for their extensive electronic delocalization. The title compound crystallizes with two symmetry-independent half 4,4'-bipyridine-1,1'-diium (bpyH2(2+)) cations and two symmetry-independent 1,1,3,3-tetracyano-2-ethoxypropenide (tcnoet(-)) anions in the asymmetric unit. One of the bpyH2(2+) ions is located on a crystallographic twofold rotation axis (canted pyridine rings) and the other is located on a crystallographic inversion center (coplanar pyridine rings). The ethyl group of one of the tcnoet(-) anions is disordered over two sites with equal populations. The extended structure exhibits two separate N-H···NC hydrogen-bonding motifs, which result in a sheet structure parallel to (010), and weak C-H···NC hydrogen bonds form joined rings. Two types of multicenter CN···π interactions are observed between the bpyH2(2+) rings and tcnoet(-) anions. An additonal CN···π interaction between adjacent tcnoet(-) anions is observed. Using density functional theory, the calculated attractive energy between cation and anion pairs in the tcnoet(-)···π(bipyridinediium) interactions were found to be 557 and 612 kJ mol(-1) for coplanar and canted bpyH2(2+) cations, respectively.
  4. Ng SW
    Acta Crystallogr C Struct Chem, 2021 08 01;77(Pt 8):443-448.
    PMID: 34350841 DOI: 10.1107/S205322962100663X
    Because an IUCr/IUPAC-designated set of letters/numbers identifies the configuration of the atoms linked to the PbII atom in its coordination compounds, a Ψ prefix before such as a polyhedral symbol provides useful information when its lone pair is stereochemically active. Such notation is especially relevant when the metal atom is connected to eight or more atoms regardless of whether the lone pair is active or inert. The polyhedral symbols for the crystal structures in some 50 articles published after 2000 are reported here as the original studies did not expressly identify coordination geometries.
  5. Ng SW
    Acta Crystallogr C Struct Chem, 2021 Oct 01;77(Pt 10):610-614.
    PMID: 34607983 DOI: 10.1107/S205322962100886X
    Tris(diethyldithiocarbamato-κS)antimony(III), [Sb(C5H10NS2)3], is tentatively presumed to comprise a triclinic and a monoclinic polymorph intergrown into each other. The geometry in the triclinic phase is a ψ-capped octahedron and that in the monoclinic phase is a ψ-pentagonal bipyramid. The study also identifies the polyhedral symbols for a reported pair of polymorphs of another SbIII coordination compound, as well as for those of published polymorphic modifications of other BiIII and PbII coordination compounds; the symbols in the pair differ in most of these examples. When differentiating related structures of such classes of coordination compounds, lone-pair stereochemistry may be another informative variable, as stereochemical activity is not always apparent from bond distances and angles only.
  6. Tou TY, Ng SW
    Acta Crystallogr C Struct Chem, 2021 Oct 01;77(Pt 10):586-590.
    PMID: 34607980 DOI: 10.1107/S2053229621009293
    The present report lists selected publications on centrosymmetric compounds that manifest second harmonic generation responses in a laser, along with a few publications that dispute the laser outcomes. Two studies provide a plausible explanation for this apparent contradiction between second-order nonlinear susceptibility and inversion symmetry: the crystals are noncentrosymmetric and are twinned by inversion. If crystal structures of SHG-active compounds are presented in centrosymmetric settings, the authors of the publications may consider stipulating that the true space group is likely to be one of the noncentrosymmetric sub-space groups.
  7. Mark-Lee WF, Chong YY, Kassim MB
    Acta Crystallogr C Struct Chem, 2018 09 01;74(Pt 9):997-1006.
    PMID: 30191891 DOI: 10.1107/S2053229618010586
    The crystal and molecular structures of two ReI tricarbonyl complexes, namely fac-tricarbonylchlorido[1-(4-fluorocinnamoyl)-3-(pyridin-2-yl-κN)pyrazole-κN2]rhenium(I), [ReCl(C17H12FN3O)(CO)3], (I), and fac-tricarbonylchlorido[1-(4-nitrocinnamoyl)-3-(pyridin-2-yl-κN)pyrazole-κN2]rhenium(I) acetone monosolvate, [ReCl(C17H12ClN4O3)(CO)3]·C3H6O, (II), are reported. The complexes form centrosymmetric dimers that are linked into one-dimensional columns by C-H...Cl and N-O...H interactions in (I) and (II), respectively. C-H...Cl interactions in (II) generate two R21(7) loops that merge into a single R21(10) loop. These interactions involve the alkene, pyrazole and benzene rings, hence restricting the ligand rotation and giving rise to a planar conformation. Unlike (II), complex (I) exhibits a twisted conformation of the ligand and a pair of molecules forms a centrosymmetric dimer with an R22(10) loop via C-H...O interactions. The unique supramolecular structures of (I) and (II) are determined by their planarity and weak interactions. The planar conformation of (II) provides a base for appreciable π-π stacking interactions compared to (I). In addition, an N-O...π interaction stabilizes the supramolecular structure of (II). We report herein the first n→π* interactions of ReI tricarbonyl complexes, which account for 0.33 kJ mol-1. Intermolecular C-H...Cl and C-H...O interactions are present in both complexes, with (II) showing a greater preference for these interactions compared to (I), with cumulative contributions of 48.7 and 41.5%, respectively. The influence of inductive (fluoro) and/or resonance (nitro) effects on the π-stacking ability was further supported by LOLIPOP (localized orbital locator-integrated π over plane) analysis. The benzene ring of (II) demonstrated a higher π-stacking ability compared to that of (I), which is supported by the intrinsic planar geometry. The HOMA (harmonic oscillator model of aromaticity) index of (I) revealed more aromaticity with respect to (II), suggesting that NO2 greatly perturbed the aromaticity. The Hirshfeld fingerprint (FP) plots revealed the preference of (II) over (I) for π-π contacts, with contributions of 6.8 and 4.4%, respectively.
  8. Chia TS, Quah CK
    Acta Crystallogr C Struct Chem, 2016 Dec 01;72(Pt 12):971-980.
    PMID: 27918299
    As a function of temperature, the hexamethylenetetramine-2-methylbenzoic acid (1/2) cocrystal, C6H12N4·2C8H8O2, undergoes a reversible structural phase transition. The orthorhombic high-temperature phase in the space group Pccn has been studied in the temperature range between 165 and 300 K. At 164 K, a t2phase transition to the monoclinic subgroup P21/c space group occurs; the resulting twinned low-temperature phase was investigated in the temperature range between 164 and 100 K. The domains in the pseudomerohedral twin are related by a twofold rotation corresponding to the matrix (100/0-10/00-1. Systematic absence violations represent a sensitive criterium for the decision about the correct space-group assignment at each temperature. The fractional volume contributions of the minor twin domain in the low-temperature phase increases in the order 0.259 (2) → 0.318 (2) → 0.336 (2) → 0.341 (3) as the temperature increases in the order 150 → 160 → 163 → 164 K. The transformation occurs between the nonpolar point group mmm and the nonpolar point group 2/m, and corresponds to a ferroelastic transition or to a t2structural phase transition. The asymmetric unit of the low-temperature phase consists of two hexamethylenetetramine molecules and four molecules of 2-methylbenzoic acid; it is smaller by a factor of 2 in the high-temperature phase and contains two half molecules of hexamethylenetetramine, which sit across twofold axes, and two molecules of the organic acid. In both phases, the hexamethylenetetramine residue and two benzoic acid molecules form a three-molecule aggregate; the low-temperature phase contains two of these aggregates in general positions, whereas they are situated on a crystallographic twofold axis in the high-temperature phase. In both phases, one of these three-molecule aggregates is disordered. For this disordered unit, the ratio between the major and minor conformer increases upon cooling from 0.567 (7):0.433 (7) at 170 K via 0.674 (6):0.326 (6) and 0.808 (5):0.192 (5) at 160 K to 0.803 (6):0.197 (6) and 0.900 (4):0.100 (4) at 150 K, indicating temperature-dependent dynamic molecular disorder. Even upon further cooling to 100 K, the disorder is retained in principle, albeit with very low site occupancies for the minor conformer.
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